data from geometrical coordinates ??

I am trying to find out if there is a way in a UDF to specify solver data (ie; velocity values) in terms of coordinate values (x,y,z) instead of cell or face indices.

Clearly, FLUENT itself can do this when for example, we do an XY plot of a variable along a line. The question is, what kind of macro names may exist that would readily enable doing this for post-processing analysis??